1. Field of the Invention
The present invention relates to a display system capable of displaying images in the single and dual image modes and more particularly, to a display system that switches automatically from the single image mode to the dual image mode, and vice versa.
2. Description of the Related Art
Conventionally, display systems capable of displaying images in the dual image mode where two images are simultaneously displayed on the same screen are known. An example of the systems of this type is disclosed in the Japanese Non-Examined Patent Publication No. 58-21981 published in 1983. In this system, a television (TV) picture tube having the dual image mode is used. Usually, an ordinary TV program is displayed in a larger display area on the screen of the tube while a piece of information (e.g., an acceptance or reception number) sent from a computer is displayed in a smaller display area on the same screen, The smaller display area is designed for displaying a competing TV program on a different channel from the larger display area.
When the user presses an operating button connected to the computer, a switching signal is sent to the system from the computer, thereby switching the image in the larger display area with the image in the smaller display area, and vice versa. Specifically, another piece of information (e.g., another acceptance or reception number) sent from the computer is displayed on the larger display area while the TV program is displayed on the smaller display area. After a specific period of time passes, the images on the larger and smaller areas are replaced with each other, returning to the original display state.
With the conventional display system disclosed in the Publication No. 58-21981, as explained above, the larger and smaller display areas are always formed on the screen of the TV picture tube and therefore, there is a disadvantage that the smaller area is kept blank (e.g., blue back) when there is no information to be displayed on the smaller area.
To avoid this advantage, the dual image display function may be activated only within a necessary period of time. Specifically, when the user presses the operation button, a specific switching signal is sent from the computer to the TV tube, thereby switching the display state on the screen from the single image mode to the dual image mode. In this case, a piece or information from the computer is displayed on the smaller area while the TV program is displayed on the larger area.
However, with the display system where the dual image display function is activated or switched only within a necessary period of time, a specific switching signal needs to be inputted into the TV picture tube. Thus, when video information is sent to the tube from an input device such as a Video Cassette Recorder (VCR) instead of the TV programs, a controller for generating the switching signal is required. Also, proper connection terminals for the switching signal need to be mounted on the system and at the same time, the terminals need to be connected to a circuit for decoding the switching signal and for switching the state of the screen between the single and dual image modes.
Moreover, the controller and the tube need to be connected with each other by way of a cable dedicated to the switching signal in addition to connection of ordinary video cables. This makes the configuration of the system complicated and the connectable distance limited.
On the other hand, the Japanese Non-Examined Patent Publication No. 2000-41196 published in February 2000 discloses a technique for detecting the existence and absence of the synchronizing signal of video inputs supplied through a plurality of input lines in a TV picture tube. In this technique when the video input contains a synchronizing signal, Information for representing the images being displayable is displayed on the screen of the tube. When the video input contains no synchronizing signal, information for representing the images being non-displayable is displayed on the screen.
With the technique disclosed in the Publication No. 2000-41196, the user recognizes which video inputs arc displayable and non-displayable from the content pf the information displayed on the screen. Therefore, the user can skip the non-displayable inputs. This means that the user can choose a desired one of the inputs while decreasing the necessary number of operations.
A technique to judge whether or not images are displayable on the screen by detecting a synchronizing signal in the video input is disclosed in, for example, the Japanese Non-Examined Patent Publication Nos. 64-23282 published in 1929, 5-244450 published in 1993, 10-69254 published in 1998, and 10-301522 published in 1998.
By the way, the Publication No. 2000-41196 does not disclose the technique about the switching operation between the single image mode and the dual image mode. However, supposing that the switching operation be incorporated into the technique, the technique will be modified in the following way.
The existence and absence of the synchronizing signal of video signals supplied through a plurality of video inputs is detected in a TV picture tube. When the video input contains a synchronizing signal, information for representing their images being displayable is displayed on the screen or the tube When the video input contains no synchronizing signal, information for representing the images being non-displayable is displayed on the same screen. Moreover, when two ones of the inputs having displayable images are selected, the images sent through the two inputs are displayed on the screen in the dual mode. When only one of the inputs having displayable images is selected, the images sent through the input are displayed on the screen in the single mode.
In this modified technique, the selection and indication of the desired video inputs need to be conducted by the user himself as necessary. This leans that the switching operation between the single and dual image modes would be not carried out automatically
Accordingly, an object of the present invention is to provide a display system that makes it possible to switch automatically from the single image mode to the dual image mode, and vice versa.
Another object of the present invention is to provide a display system that makes it possible to switch from the single image mode to the dual image mode without input of any switching signal, and vice versa.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
According to a first aspect of the present invention, a display system is provided. This system comprises.
(a) a first detector for detecting a synchronizing signal of a first video input sent through a first input line;
the first detector outputting a first detection signal when the synchronizing signal of the first video input is detected;
(b) a second detector for detecting a synchronizing signal of a second video input sent through a second input line;
the second detector outputting a second detection signal when the synchronizing signal of the second video input is detected;
(c) a switch for selecting one of a single image mode and a dual image mode;
the switch selecting the single image mode when receiving one of the first detection signal outputted from the first detector and the second detection signal outputted from he second detector, thereby producing a first output signal;
the first output signal corresponding to one of the first video input and the second video input received by the switch;
the switch selecting the dual image mode when receiving both of the first detection signal outputted from the first detector and the second detection signal outputted from the second detector, thereby producing a second output signal;
the second output signal corresponding to both of the first video input and the second video input received by the switch; and
(d) a display device for displaying an image according to the first or second video input on a screen in the single image mode and two images according to the first and second video inputs on the screen in the dual image mode.
With the display system according to the first aspect of the present invention, for example, it is supposed that an image is displayed on the screen of the display device in the single image mode according to the first video input sent through the first input line. At this time, the first detector outputs the first detection signal. Thereafter, if the second detector detects the synchronizing signal of the second video input sent thorough the second input line, the second detector outputs the second detection signal This means that the switch receives both of the first and second detection signals in this state. As a result, the switch selects the dual image mode and accordingly, the two images are simultaneously displayed on the screen of the display device according to the first and second video inputs.
As explained above, because of the detection of the synchronizing signal of the second video input by the second detector, the display device is automatically turned to the dual image mode from the single image mode. If the synchronizing signal of the second video input disappears in this state, the display device is automatically turned to the single image mode from the dual image mode, thereby displaying only the image according to the first video input sent through the first input line.
Thus, the display device can be switched automatically from the single image mode to the dual image mode, and vice versa. This switching operation does not require the input of any switching signal.
In a preferred embodiment of the display system according to the first aspect, each of the synchronizing signals of the first and second video inputs is a pulsed signal. When the pulsed signal is not observed within a specific period of time, each of the first and second detectors judges that each of the first and second video inputs does not include the corresponding synchronizing signal.
In another preferred embodiment of the display system according to the first aspect, each of the synchronizing Signals of the first and second video inputs is a pulsed signal. When the pulsed signal observed within a specific period of time has a frequency apart sufficiently from an available frequency of the display device, each of the first and second detectors judges that each of the first and second video inputs does not include the corresponding synchronizing signal.
According to a second aspect of the present invention another display system is provided. This system comprises
(a) an input line selector for selecting two ones of n input lines as a first input line and a second input line, where n is an integer equal to or greater than 3;
(b) a first detector for detecting a synchronizing signal of a first video input sent through the first input line;
the first detector outputting a first detection signal when the synchronizing signal of the first video input is detected;
(c) a second detector for detecting a synchronizing signal of a second video input sent through the second input line;
the second detector outputting a second detection signal when the synchronizing signal of the second video input is detected;
(d) a switch for selecting one of a single image mode and a dual image mode;
the switch selecting the single image mode when receiving one of the first detection signal outputted from the first detector and the second detection signal outputted from the second detector, thereby producing a first output signal;
the first output signal corresponding to one of the first video input and the second video input received by the switch;
the switch selecting the dual image mode when receiving both of the first detection signal outputted from the first detector and the second detection signal outputted from the second detector, thereby producing a second output signal;
the second output signal corresponding to both of the first video input and the second video input received by the switch; and
(e) a display device for displaying an image according to the first or second video input on a screen in the single image mode and two images according to the first and second video inputs on the screen in the dual image mode.
With the display system according to the second aspect of the present invention, the input line selector selects two ones of the n input lines as the first and second input lines. The other configuration and operation are substantially the same as those of the display system according to the first aspect. As a result, there are the same advantages as those of the system according to the first aspect.
In a preferred embodiment of the display system according to the second aspect, each of the synchronizing signals of the first and second video inputs is a pulsed signal When the pulsed signal is not observed within a specific period of time, each of the first and second detectors judges that each of the first and second video inputs does not include the corresponding synchronizing signal.
In another preferred embodiment of the display system according to the second aspect, each of the synchronizing signals of the first and second video inputs is a pulsed signal then the pulsed signal observed within a specific period of time has a frequency apart sufficiently from an available frequency of the display device, each of the first and second detectors judges that each of the first and second video inputs does not include the corresponding synchronizing signal.